The Network Layer Chapter 5 Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Network Layer Design Isues Store-and-Forward Packet Switching Services Provided to the Transport Layer Implementation of Connectionless Service Implementation of Connection-Oriented Service Comparison of Virtual-Circuit and Datagram Subnets Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Routing Algorithms The Optimality Principle Shortest Path Routing Flooding Distance Vector Routing Link State Routing Hierarchical Routing Broadcast Routing Multicast Routing Routing for Mobile Hosts Routing in Ad Hoc Networks Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Routing Algorithms (2) Conflict between fairness and optimality. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

The Optimality Principle (a) A subnet. (b) A sink tree for router B. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Shortest Path Routing The first 5 steps used in computing the shortest path from A to D. The arrows indicate the working node. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Distance Vector Routing (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Distance Vector Routing (2) The count-to-infinity problem. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Link State Routing Each router must do the following: 1.Discover its neighbors, learn their network address. 2.Measure the delay or cost to each of its neighbors. 3.Construct a packet telling all it has just learned. 4.Send this packet to all other routers. 5.Compute the shortest path to every other router. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Learning about the Neighbors (a) Nine routers and a LAN. (b) A graph model of (a). Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Measuring Line Cost A subnet in which the East and West parts are connected by two lines. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Building Link State Packets (a) A subnet. (b) The link state packets for this subnet. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Distributing the Link State Packets The packet buffer for router B in the previous slide (Fig. 5-13). Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Route Discovery a)(a) Range of A's broadcast. b)(b) After B and D have received A's broadcast. c)(c) After C, F, and G have received A's broadcast. d)(d) After E, H, and I have received A's broadcast. Shaded nodes are new recipients. Arrows show possible reverse routes. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Route Discovery (2) Format of a ROUTE REQUEST packet. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Route Discovery (3) Format of a ROUTE REPLY packet. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Route Maintenance (a) D's routing table before G goes down. (b) The graph after G has gone down. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Fragmentation (a) Transparent fragmentation. (b) Nontransparent fragmentation. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011

Fragmentation (2) Fragmentation when the elementary data size is 1 byte. (a) Original packet, containing 10 data bytes. (b) Fragments after passing through a network with maximum packet size of 8 payload bytes plus header. (c) Fragments after passing through a size 5 gateway. Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education- Prentice Hall, 2011